Serum 25-hydroxvitamin D levels, the most representative indicator of vitamin D stores, are lower in individuals who are obese or overweight than in those of normal weight, a study found.
In addition, the study showed that secondary hyperparathyroidism (SHPT) only develops when the estimated glomerular filtration rate (eGFR) is below 60 mL/min/1.73 m2, and it is universally observed in individuals with an eGFR below 30 mL/min/1.73 m2, Athanasios Kitsos, MD, the University of Ioannina in Ioannina, Greece, and colleagues reported in Hormones (2018;17;237-246).
The researchers compared 104 obese (body mass index [BMI] 30 kg/m2 or higher) or overweight (BMI 25–29.9 kg/m2) individuals with a control group of 50 normal-weight individuals (BMI less than 25 kg/m2). The investigators classified participants according to eGFR (mL/min/1.73 m2): G1, above 60; G2, 30–59; and G3, 15–29).
Levels of 25-hydroxyvitamin D were significantly lower in the G1, G2, and G3 obese/overweight individuals than in the G1, G2, and G3 normal-weight individuals (21.7 vs 26.5; 19 vs 25; and 15.8 vs 20.3 ng/mL, respectively), the investigators reported. Levels of 1,25-dihydroxyvitamin D and parathyroid hormone (PTH) were similar, however, regardless of BMI.
In all eGFR groups, mean 25(OH)D levels were below 30 ng/mL in both obese/overweight and normal-weight individuals.
PTH levels increased as eGFR decreased in both the obese/overweight and normal-weight participants, according to the researchers. SHPT began to occur at eGFR levels below 60. Among patients with an eGFR of 15–29, the obese/overweight and normal-weight groups had median PTH levels of 161 and 182 pg/mL, respectively. All patients in this eGFR group had PTH values above the reference range.
Kitsos A, Dounousi E, Kalaitzidis R, et al. Serum vitamin D in obese and overweight subjects according to estimated glomerular filtration rate. Hormones. 2018;17:237-246.